1. Field of the Invention
The present invention pertains to rethreading dies used for repairing damaged threads on screws, bolts, and similar threaded stud members. In many instances, e.g. where the damaged thread is on the end of an engine crankshaft, removal of the stud for replacement or repair is extremely impractical due to the difficulty of disassembling the device in which the stud is installed. Accordingly, it is desirable and frequently attempted to rework the damaged threads of such a stud with the stud in situ, i.e. installed in its intended position in the engine or other device. This in turn typically introduces additional problems of attempting to re-work the thread in a cramped space and with only one "free" end on the damaged member.
2. Description of the Prior Art
One common technique currently known for attempting to rework a damaged threaded stud in situ is through the use of a rethreading die in the form of a nut having a central opening for receipt of the stud member. Facing into and defining this opening are a plurality of thread forming or cutting surfaces interspersed with relieved areas which permit cuttings to fall away from the stud and rethreading die. One problem with this conventional type die is that it must be installed on the free end of the stud and worked inwardly. Frequently, the thread damage to that stud has occurred on or near the free end. Thus, the free end of the stud must be cut away and/or hand worked with a file or other simple tool to permit the die nut to be started on the free end of the stud.
Even if these hand working operations were typically successful, they would be undesirably tedious. However, in addition to this problem, the hand working operations are frequently unsuccessful in that the hand worked threads are not in perfect pitch or alignment with the remainder of the threads on the stud. Accordingly, when the die is started on the hand worked threads and moved inwardly, it will tend to remain on pitch with the hand worked threads and then cross cut and ruin the remainder of the original machined threads. In short, such conventional rethreading die nuts sometimes cause as much or more damage than they remedy.
Other common tools sometimes employed for rethreading are thread files and stock-and-die type threading tools. The former are difficult and tedious to use, as well as imprecise in their results. The latter are unduly large and cumbersome for use on in situ studs.
U.S. Pat. No. 1,488,271 to Miller discloses a modified die nut wherein one side is machined, to receive a tension type adjusting screw, and then split. The split can be widened or narrowed by adjusting the screw, which in turn adjusts the size of the central opening. This arrangement permits only fine adjustments, and does not permit the nut to be opened and emplaced on the inboard end of a damaged stud.
U.S. Pat. No. 888,563 to Wilkins discloses a hinged die. However, the external configuration of this tool would make it virtually impossible to use in situ in close spaces.
U.S. Pat. No. 1,606,186 to Shaefer et al discloses a hinged plyer-like tool suitable for hand working operations as described above.
U.S. Pat. No. 3,956,787 to Crumpacker discloses an unduly complicated collet-like tool. U.S. Pat. No. 1,857,493 to Campaigne pertains to a two-piece adjustable "thread chaser."
None of these prior devices is satisfactory for use in reworking a damaged threaded stud in situ, particularly in closely confined spaces. In particular, none of them provide a simple device, which may be easily manufactured, and which may be installed on the inboard end of a stud, even in a closely confined space, and worked outwardly to repair the damaged thread.